Maki Kaji: A Tribute

Maki Kaji called himself the godfather of sudoku, which was both accurate and modest. He did not invent the puzzle. He gave it its name, refined its rules into the version the world now plays, and built the magazine that nurtured a community of constructors around it. Without him, sudoku stays a Dell magazine curiosity called Number Place.

He died in August 2021 at the age of 69, of bile duct cancer, in Tokyo. The obituaries called him the man who gave puzzles a home. They were not exaggerating.

How he found the puzzle

The story Kaji told in interviews was simple. He picked up an American puzzle magazine in the early 1980s, encountered Number Place, and thought it had been imperfectly named. The rules deserved a better label. He took the puzzle to his magazine and started running it.

The renaming came in 1986. "Sudoku" (数独) is a contraction of "sūji wa dokushin ni kagiru" — the digits are limited to one occurrence. The phrase describes the puzzle's central rule and compresses neatly into two characters. Kaji had a constructor's ear for the right name. The label has not changed since.

What he ran Nikoli to be

Nikoli under Kaji was not a profit-maximising business. It was a craft house. The puzzles were constructed by hand. Constructors were named on every grid. The editorial standards were unforgiving: every puzzle had to be solvable by deduction, with a unique solution, and with rotational symmetry in its clue placement. The standards meant Nikoli could produce fewer puzzles than competitors, but the ones it produced felt better.

Kaji believed the feel of a puzzle mattered more than its difficulty. A puzzle that was hard but tedious was not a good puzzle. A puzzle that was easy but elegant was. That philosophy shaped every Nikoli release for forty years.

"I am not in the puzzle business. I am in the business of giving people a small piece of beauty before they go to bed."

What he gave away

When sudoku exploded globally in 2004 and 2005, Kaji could have sued for trademark or licensed the name aggressively. He did not. The name "sudoku" had not been registered as a trademark in most countries, and Kaji decided not to pursue the registrations he could have. He felt the puzzle had grown beyond Nikoli, and his job was to celebrate that, not to capture rents from it.

That decision cost Nikoli a fortune. Friends and colleagues often pointed it out. Kaji's reply was always some version of the same thing: the puzzle was bigger than the magazine, and the puzzle's spread was its own reward.

The constructor he was

Kaji constructed puzzles himself, occasionally. The Nikoli magazine ran his work under the pen name Kaji Maki. The puzzles were almost always elegant rather than difficult, with clean symmetric clue placements and a single advanced technique gently introduced. They reflect his taste.

He insisted that no Nikoli puzzle should ever require guessing. Every puzzle had to be a logic exercise, solvable by deduction alone. The principle is the reason "no guessing required" is now a standard quality marker for sudoku worldwide. Kaji put it there.

His last public appearances

Kaji travelled to sudoku championships well into his sixties. He attended the World Sudoku Championship in Lucca in 2006, the Beijing championship in 2013, and gave a memorable talk in 2018 about why constructors matter more than software. He was gentle, funny, and almost embarrassingly modest about his role.

Solvers who met him remember being treated as peers. He asked about their favourite techniques. He took notes. He sent thank-you cards. The community that mourns him still keeps the cards.

For more on the magazine he ran, see inside Nikoli. For the American chapter of the same story, see Howard Garns and Number Place.